In the art, it is known to arrange the magnets in a permanent magnetized synchronous machine so as to cause the magnetic flux to flow in paths at right angles to the direction of rotation of the rotor. A machine of this type, designed according to what is called the transverse flux principle, is illustrated in FIG. 1. The rotor of such a machine is made up of permanent magnets of alternate polarity. The magnets are secured to bars of magnetic material which serve as magnetic return conductors. The stator consists of U-shaped stator elements of magnetic material, the number of which is equal to half the number of magnets. The stator winding is designed as a ring winding. This means that, if the distance between the magnet bars, known as the pole pitch, is small, the copper volume per stator element becomes small, like the copper losses.
When the rotor is in a given position, the magnetic flux flows through all the stator elements in the same direction. When the rotor has rotated through one pole pitch, the direction of the flux through the stator elements has been reversed. When the rotor has rotated through another pole pitch, the direction of the flux through the stator elements has again been reversed. Thus, the flux through the ring winding accomplishes one cycle as the rotor rotates through two pole pitches.
As compared with a machine of the longitudinal flux type, the transverse flux machine of the invention offers the following advantages:
The cross-sectional area of the magnetic flux is practically constant throughout the path of flux. The iron losses in such a machine therefore are smaller than in a longitudinal machine, where locally, especially in the tooth area, the flux density is considerably higher than in the rest of the magnetic circuit. PA1 In a transverse flux machine, the active amount of copper, consisting of the copper ring between the stator elements, is considerably smaller than in a longitudinal machine where the inactive amount of copper consists of the coil ends.
Thus, the transverse flux machine represents, in terms of weight and volume, an energy-dense machine of high efficiency. The shorter the pole pitch is, the smaller becomes the active amount of copper and the higher the efficiency.